Motor driven vehicles such as hybrid vehicles and electric vehicles use regenerative braking to improve fuel efficiency. The regenerative braking system converts kinetic energy of a vehicle into electrical energy during braking of the vehicle and stores it in a battery, and uses the electric energy stored in the battery as kinetic energy of the vehicle when the vehicle travels, thereby enhancing fuel efficiency. In order to implement such a regenerative braking system, regenerative braking cooperative control technology for controlling the sum of regenerative braking torque generated in a motor during regenerative braking and friction braking torque generated in brakes to be equal to driver's request braking torque is required.
There is occurred a so-called blending section in regenerative braking cooperation control, i.e., a section in which the regenerative braking torque decreases and the friction braking torque increases. There is occurred in this blending section a phenomenon that the friction braking torque is increased due to increase of a frictional coefficient of a friction pad and hence deceleration of a vehicle is increased. The reason why this phenomenon occurs larger in regenerative braking vehicles than in ordinary vehicles is because a change in braking deceleration occurs due to a change in the friction coefficient of the pad. That is, deceleration is maintained at a constant level in a conventional brake system in which regenerative braking is not performed, as shown in FIG. 1a, while there is occurred in the regenerative braking system a blending section in which deceleration of the vehicle increases, as shown in FIG. 1b. Therefore, in the blending section, the friction braking torque increases and hence the friction coefficient of the pad increases so that the braking torque changes largely, with the result that a driver feels discomfort at the time of braking as the braking deceleration changes. The discomfort occurs more in a section where the friction braking torque increases than in a section where the friction braking torque is decreased or small.
Further, there is occurred a large change in deceleration at the time point when a vehicle stops as shown in FIG. 2. Since the occurrence of such a large change in deceleration, that is, jerk gives great discomfort to the driver, it is necessarily required to prevent the jerk phenomenon at the time of stopping the vehicle in order to improve merchantability of vehicles.
Patent Document Korean Laid-Open Patent Publication No. 10-2016-0056530 (issued on May 20, 2016) and counterpart U.S. Pat. No. 9,533,581 (issued on Jan. 3, 2017) are related to subject matter disclosed herein.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.